Mold gates of various designs are used to control the flow of molding compound into and out of a molding chamber through a sprue aperture in typical injection molds and the like. See for example Von Holdt U.S. Pat. Nos. 4,380,422; 4,289,468; and 4,289,473.
Various disadvantages accompany the various designs of prior art molds and their gates. For example, the mold gate structure of the previously cited U.S. Pat. No. 4,380,422 utilizes a longitudinal flexing system which is expensive and difficult to manufacture, and which also exhibits an undesirable amount of metal fatigue during operation which limits its useful life. The mold gate of U.S. Pat. No. 4,289,468 utilizes a pressure driven sliding member to open and close a mold gate, but it also exhibits a tendency to stick during operation because of the seepage of molding compound between the sliding surfaces of the sliding plunger used therein and the bore that retained it. Finally, the mold of U.S. Pat. No. 4,289,473 exhibits no means at all for preventing back flow of molding compound out of the molding chamber, and in some circumstances generates weakened areas in the molded product immediately adjacent to the mold gate.
In accordance with this invention, a mold gate is provided which overcomes the above disadvantages, in that it is relatively inexpensive to manufacture, exhibits a long useful life with minimum metal fatigue caused by flexing, and which is substantially free of the possibility of failure to operate through sticking in position, because the mold gate can be free of sliding moving parts. Nevertheless, back flow of molding compound out of the molding chamber or cavity may be controlled, for improved production of quality molded parts.